keypress event on display button by keyboard click [on hold]

needs to activation html button

<td> <input name="Eight" type="Button" class="Gray" value="8" onclick='take("8")' /></td>

by keyboard event, how can I do this?

What mean key in keydownFunction(key)? and doSomething() is function instead take("8") in onclick= ? Really dull questions but I'm really don't understand system to call by keyboard events %)